Sorption is a physical and chemical process by which a substance (typically a gas or liquid) accumulates within another phase or on the phase boundary of two phases. Depending on the place of accumulation, a differentiation is made between absorption (accumulation in a phase) and adsorption (accumulation at the phase boundary).
The reverse process is called desorption.
The figure below shows two sorption-desorption cycles on a zeolite sample. The zeolite sample was treated with atmospheric cycles between wet and dry nitrogen gas flows. During the injection of a wet gas flow, the sample exhibits a distinct mass increase which is a result of the water absorption within the zeolite network, whereas during the dry gas flow, desorption takes place. The graph presented shows that the water absorption of a zeolite is a totally reversible process.